Abnormal regulation of apoptosis is now recognized to play an important role in the development of cancer. The apoptosis pathway can be initiated by various extracellular and intracellular stresses, including growth factor deprivation, DNA damage, oncogene induction, and cytotoxic drugs (Danial, N. N. and Korsmeyer, S J. Cell (2004) 116, 205-219). The death signal leads to the oligomerization of the pro-apoptotic proteins Bax and Bak. Upon activation, they permeabilize the mitochondrial outer membrane and release apoptogenic factors into the cytoplasm. This process is tightly regulated by both pro-apoptotic (Bax, Bak, Bad, Bid, Bim, Bmf, NOXA, PUMA) and anti-apoptotic (Bcl-2, Bcl-xL, Bcl-w, Bcl2-A1, Mcl-1) members of the Bcl-2 family of proteins. Recent data suggests that the anti-apoptotic Bcl-2 proteins function to protect the cell from apoptotic insults, primarily by preventing disruption of mitochondrial outer membrane integrity by binding to the pro-apoptotic proteins as described in Adams, J. M. and Cory S. Oncogene (2007) 26, 1324-1337; Willis, S. N. et al. Science (2007) 315, 856-859. Because tumor cells are under stress, alterations in their apoptotic signaling pathways are believed to be crucial for survival. Recent data implicates down-regulated apoptosis in the onset of cancer. Research has shown, for example, that anti-apoptotic proteins, are over-expressed in many cancer cell types as described in Beroukhim, R. et al. Nature (2010) 463, 899-905; Zhang J. Y., Nature Reviews Drug Discovery, (2002) 1, 101; Kirkin, V. et al. Biochimica et Biophysica Acta (2004) 1644, 229-249; and Amundson, S. A. et al. Cancer Research (2000) 60, 6101-6110. This dysregulation results in the survival of cells that would otherwise have undergone apoptosis such as cancer cells. This suggests that neutralizing the function of anti-apoptotic Bcl-2 proteins may offer an effective strategy for the elimination of cancer cells. In addition, resistance to chemotherapy which is a major cause of treatment failure and poor prognosis in many cancers can be caused by the upregulation of anti-apoptotic Bcl-2 family proteins.
An important anti-apoptotic member of the Bcl-2 family is Myeloid cell leukemia-1 (Mcl-1). Mcl-1 is one of the most frequently amplified anti-apoptotic genes in human cancers including prostate, lung, pancreatic, breast, ovarian, and cervical cancers, as well as melanoma, B-cell chronic lymphocytic leukemia (B-CLL), acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) (Beroukhim et al. Nature (2010) 463, 899-905). Moreover, its overexpression is implicated as a resistance factor for multiple therapies including widely prescribed microtubule-targeted agents for breast cancers, such as paclitaxel and vincristine as well as Gemcitabine, a first-line treatment option for pancreatic cancer (Wei et al. Cancer Chemother Pharmacol (2008) 62, 1055-1064 and Wertz et al. Nature (2011) 471, 110-114). These data suggest that Mcl-1 is an important target for a wide variety of cancers.
In many cancer cell types, the cancer cell's survival is attributed to the dysregulation of the apoptotic pathway caused by the over-expression of one or more anti-apoptotic Bcl-2 protein family members. Because of the important role for Bcl-2 family of proteins in regulating apoptosis in both cancerous and non-cancerous cells, and the inter-cell variability of Bcl-2 family protein expression, it could be advantageous to have a small molecule inhibitor that selectively targets and preferably binds to one type or a subset of anti-apoptotic Bcl-2 protein(s). A selective compound also may confer certain advantages in the clinical setting, by providing flexibility to select a dosing regimen to reduce on-target toxic effects in normal cells.
Because Mcl-1 protein is an important Bcl-2 family member associated with a number of diseases, there is a need for compounds which bind to and inhibit the activity of Mcl-1 protein.